Method of coating metals



le Patented Sept. 9, 1941 STATES PATENT' OFFICE Charles A. Medeker and Menahem Merlnb-Sobel, Cleveland Heights, Ohio, assignors to William L. Uimer, Cleveland, Ohio I 1 NoDrawlng.

2Claims.

This invention relates to the coating of metal on-metal bases, and, in particular, tocomposite layers of metals-.'. Such metal composites are often also known as clad metals.

Although many metals can be electro deposited onto other metals such electro deposition is not economically feasible when moderately thick coatings are desired. As an example, we may cite the fact that copper or brass coated steel sheet,.with the coating representing about of the. total, has'great potential commercial demand, but electro deposition methods are much too expensive forpractical operation. In addition to such combinations as are technically feasible, though commercially unprofitable, there is a large number of metals which, by their very nature, cannot be eiectro deposited, for example, stainless steel, etc.

Such coatings, or composite metals have occa- I sionally been made in the past from massive metal by the simultaneous rolling of carefully cleaned and machined slabs of the two metals, rolled face to face at high temperature. However, the practical difllculties standing inthe way of such co-rolling are numerous, and have made the use of this process quite expensive where it is at all feasible; in many instances it is, to all intents and purposes, commercially unworkable altogether. Copper :or brass coating of steel, already cited, is one case where the simultaneous rolling of. metal slabs hasproven ineffective. This is probably'due to the fact that copper and iron have little if any alloying tendencies at the temperature necessaryforlthe operation. In this connection, it-is worthy of note that those cases where the present methodof'co-roliing of slabs is moderately successful te'chnically are represented by metalswhichare easily alloyed with irone. g., nickel-and which have relatively high melting points, so as to enable th co-roliing to take place at temperature high enough to effect, simultaneously, surface alloying.

It is obvious that, to obtain most eflicient bonding between the two metals, it would be far more desirable thatone of the metals-preferably the one. smaller in volume quantity-pass through theiused-state. :whenphowever, attempts are 'madetoflow molten-copper or brass onto a steel base, the copper or brass collects in large globules,much' as:wouid mercury on a glass surface, and-there is no coverage of the steel. This, in

paraphrase, reflectsa failure of the cuprous metal towetthesteei surface. Theoretically, the addition' ofa flux, suchjasborax, to the steel surface-priorto flowing the copper or brass should Application March 25, 1939, Serial No. 264,178

sufflce to eflect a wetting action between the metals, but practical difllculties are great. It hasproven practically impossible, specifically, to bring the proper quantity of flux to each unit of area, and almost as difficult is controlling the flow of th flux with respect to the steel base. Comparatively little progress, therefore, has been made along these lines, and what few composite metals are to be found commercially today are being made by the co-rolling of solid slabs rather than through the pouring-on of one metal, in fused form, on another in solid form.

Our invention, by making possible the wetting of the base metal by the fused cladding metal, removes the fundamental barrier to commercial operation of this method of cladding, and permits the forming of composite ingots which can subsequently be co-roiled as a single unit. In our invention, we subject the base metal, which at all times remains in the unfused state, to the action of a vaporized flux of the type to be elucidated below, and, while such base is under the protection of such flux, the second, or cladding metal is contacted, in fused form, with the surface of the base metal.

As an example, we can again consider the coating of steel with copper. Aslab of steel about one inch in thickness is subjected to an oxyacetylene flame carrying, by entrainment, a volatile flux like methyl borate, either pure or as the methanol azeotrope. While the steel is under the influence of such oxyacetylene flame and the entrained flux, copper in the form of small pellets is dropped into the heated zone. Immediately upon melting, these copper pellets flow into continuous sheet-like form, with perfect wetting of the steel base and consequently equally perfect adhesion to it. As each unit of area is covered with copper, the flame is moved on to a fresh zone, and the process repeated until the whole surface is covered. The thickness of the copper coating can, of course, be easily regulated by increasing the quantity of copper per unit area. We have found it difficult to obtain a consistently thin coating less than about th of an inch in thickness, and prefer coatings of greater thickness than this. After the copper has been completely flowed on the steel, the resulting composite steel-copper unit is ready forrolling by the usual technics.

It is obvious that the steel may first be coated on one side, and then on the other, thus forming a sandwich" of steel, protected .by copper on both sides.

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wwlylmeuecomface of the sleb and metel. in solid, finely case, an auxiliary feed tube is n vey thevaporizable flux either alone as such 

